Land-based navigation using on-the-fly elevation assessments

ABSTRACT

Real time navigation assistance is provided on multi-level roadways using on-the-fly elevation determinations obtained by measuring the ambient air pressure. Absolute air pressure measurements adjusted to sea level (QNH) are obtained by on-the-fly wireless searches. A navigation device ( 10 ) calculates its current elevation above sea level as a function of the measured ambient actual pressure and a selected local QNH reading. This elevation is correlated to a digital map so that the navigation device ( 10 ) can be accurately located relative to a multi-level roadway. Elevation readings along any road segment ( 14 ) can be transmitted to a map update center for the purpose of updating and improving digital map data.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 61/240,253 filed 7 Sep. 2009, the entire disclosure of which is hereby incorporated by reference and relied upon.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to navigation devices of the type used by motorists and travelers, and more particularly toward an improved method for on-the-fly elevation determinations in combination with digital maps.

2. Related Art

Navigation devices like that shown at 10 for example in FIG. 1 utilize digital maps combined with accurate positioning data transmitted from a constellation of satellites or other data streams. Such GPS-enabled navigation devices may include portable, personal units such as those manufactured by TomTom N.V. (www.tomtom.com), as well as those which are integrated into an automobile instrument system, or other handheld devices, mobile phones, PDAs, and the like. These devices have been developed for many land-based navigation applications. Typically, the navigation system 10 includes a display screen 12 that portrays a portion of a stored digital map as a network of roads 14 and possibly other features such as directional signs, nearby landmarks, lane indicators, etc. A traveler having access to a GPS-enabled navigation device 10 is generally located on the digital map close to or with regard to a particular road 14.

The effectiveness of such navigation systems 10 is inherently dependent upon accurately and quickly matching the actual, real-world location of the navigation device (i.e., its geo-position) to a corresponding portion of the digital map. Navigation devices are not typically configured to measure elevation relative to sea level. Currently used GPS systems are typically less accurate in the vertical directions and better in the two horizontal axes. Nonetheless, some navigation situations cannot be accurately accomplished without knowing the current altitude of the vehicle combined with the elevation of the nearby road network 14. For example, one road segment may overlap another road segment in multi-layer road situations, complex motorway interchanges (FIG. 2), some exits and parallel roads close to a main road, multi-level parking garages, and on certain bridges, to name a few. In these situations, if the navigation system cannot discern which particular road segment a driver is currently traveling, it may not provide accurate navigation assistance.

Some navigation products have been specially equipped to discern real-time elevations using three-dimensional gyroscopic devices which are very accurate, but these systems are prohibitively expensive. Furthermore, sensitive gyroscopic calibrations must be continuously made on these devices to avoid undesirable temperature influences.

Accordingly, there is a need in the art to provide real-time navigation assistance on land-based vehicular roadways from which accurate elevation determinations can be made, on-the-fly, in situations where multi-layer roads and overlapping road segments exist. There is a need for such navigation devices to be relatively low cost and maintenance free.

SUMMARY OF THE INVENTION

This invention provides a real time navigation assistance method for land-based vehicular roadways using on-the-fly elevation determinations. According to this method, a digital road map is provided having a representation of a road network corresponding to a plurality of roads in reality. Each road in reality has a measurable elevation above sea level at any given geo-position therealong. A mobile navigation device is provided which is interactive with the digital map. The navigation device is capable of determining its instantaneous geo-position in the digital road network relative to the road in reality. As the navigation device is transported along a road in reality, its corresponding geo-position is updated in the digital road network. An on-the-fly search for local atmospheric pressure readings (QNH) is conducted via wireless transmission. A reliable local absolute atmospheric pressure reading at sea level is selected from the search results. Furthermore, the actual ambient atmospheric pressure is measured. A current road elevation is calculated as a function of the measured actual and selected absolute pressures. The calculated current road elevation is then associated with the corresponding instantaneous geo-position of the navigation device.

Using a wireless on-the-fly search for local atmospheric pressure readings (QNH), a fairly accurate elevation determination can be made as a function of the measured actual ambient atmospheric pressure. The invention provides a lower cost and more robust solution than prior art attempts using gyroscopes.

In another application of this invention, road elevation data gathered through this process is transmitted to a map update center to improve existing map data as well as other functionalities including, but not limited to, link cost attributes used in routing programs.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will become more readily appreciated when considered in connection with the following detailed description and appended drawings, wherein:

FIG. 1 is an enlarged, exemplary view of a compact, portable navigation system according to one embodiment of this invention including a display screen for presenting map data information to a vehicle driver for example;

FIG. 2 is an exemplary view showing a complex motorway interchange wherein numerous road segments are layered one upon another;

FIG. 3 is a simplified chart describing the predictable decrease in air pressure as a function of altitude above sea level;

FIG. 4 is a simplified flow chart describing one preferred embodiment of this invention;

FIG. 5 is a simplified view of a navigation device configured with an altimeter and wirelessly searching the internet to find a local absolute atmospheric pressure reading (QNH) for instance from a nearby airport;

FIG. 6 is a highly simplified, side elevation showing a four layered roadway supporting traffic flow in multiple directions, such as may be found in a parking garage for example;

FIG. 7 is a schematic view illustrating one method by which a feedback loop can be added to transmit recorded absolute altitudes in the map database to a map update center; and

FIG. 8 shows a hypothetical section of digital map combined with elevation measurements obtained therealong using principles of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the figures, wherein like numerals indicate like or corresponding parts throughout the several views, a personal navigation device 10 is shown in FIG. 1 having a display screen 12 representing a portion of a digital map containing road segments 14 as described previously. The navigation device 10 may be an in-dash system in a motor vehicle, as well as any personal, portable or handheld device appropriately enabled with position determining features including cell phones, PDAs, and the like. This invention is particularly adapted for land-based applications wherein multi-layer roadways exist. These multi-layer roadways may comprise an interchange of motorways such as shown in FIG. 2, for example, or a multi-level parking garage as shown in FIG. 4, an “over/under” bridge, or any other scenario where at least one roadway overlies another roadway such that navigation can be improved by knowing the absolute altitude of the vehicle transporting the navigation device 10.

Referring now to FIG. 3, it is known that atmospheric pressure is caused by the weight of air above a measurement point. Low pressure areas have less atmospheric mass above their location, whereas high pressure areas have more atmospheric mass above their location. As elevation of a measurement point increases there is less overlying atmospheric mass so that the pressure decreases with increasing elevation. This is described graphically in FIG. 3. It is known that atmospheric pressure decreases by approximately 0.12 mbar for every one meter of elevation. It is common in aviation applications to measure the ambient atmospheric pressure using an altimeter and then make an altitude calculation after adjusting for current atmospheric conditions. Current atmospheric conditions can change continuously, and therefore air traffic controllers and weather stations are constantly updating their local absolute atmospheric pressure readings. In aviation settings, an adjusted local absolute atmospheric pressure reading is identified by the letters QNH, which represents the local atmospheric pressure adjusted to sea level. By comparing an ambient atmospheric pressure measurement to the adjusted local QNH (supplied by a nearby airport), and then factoring a 0.12 mbar pressure differential for each meter, an airplane can fairly accurately assess their current altitude. Of course, a similar calculation can be made with different measurement units.

According to the concepts of this invention, real-time navigation assistance can be provided in connection with land-based vehicular roadways using on-the-fly elevation determinations similar to those applied in the aviation field. The navigation device 10 of this invention includes one or more digital maps stored in its memory or otherwise accessed through a suitable database connection via wireless signal. Digital road maps of this type contain a representation of road networks 14 corresponding to a plurality of roads or road segments in reality. Each road (or road segment) in reality has a measurable elevation above sea level at any given geo-position therealong. Geo-position is related to any standard geodetic system which may be used in cartography and other navigation applications, and provides a suitable coordinate frame so that a particular spot on the face of the earth can be identified with coordinates. The navigation device 10 is interactive with the digital map, together with its own position determining systems such as GPS, so as to determine its instantaneous geo-position in the digital road network relative to a road in reality. As a navigation device 10 is transported along a road 14 in reality, its corresponding geo-position is continuously updated through satellite telemetry/triangulation. Thus, data transmitted from a constellation of satellites orbiting the earth enables to navigation device 10 to determine its current geo-position which is then correlated to a road or road segment in the digital map and displayed on the display screen 12.

The navigation device 10 includes or is operatively associated with an altimeter 16 as shown in FIG. 5. The altimeter, which may be in the form of a digital barometric pressure sensor, measures the ambient atmospheric pressure in which the navigation device 10 is carried. Due to the variability of atmospheric conditions, the altimeter 16 must be calibrated regularly to reflect current local pressure conditions. Altimeter calibrations have been traditionally accomplished by adjusting a setting knob (not shown) or through a digital touch screen or keypad. Frequent re-calibrations are generally needed as local atmospheric pressures vary with temperature and the movement of pressure systems in the atmosphere. According to aviation terminology, the regional or local air pressure adjusted to mean sea level is referred to as the QNH. When an altimeter is calibrated to the current local QNH setting, it will enable calculation of the instantaneous height above sea level (i.e., the altitude or elevation).

Local absolute (i.e., adjusted for sea level) atmospheric pressure readings (QNH) are provided by many meteorological services, including almost every airport in the world, and updated on a regular basis. Update intervals of 30 minutes are common for airport information. In addition, some weather stations, local amateur weather clubs, and other organizations will provide current QNH readings for a particular location. A QNH reading provided by any source corresponds to its geo-position, and may not be entirely reliable as a reference reading for altimeter calibrations tens or hundreds of kilometers away. Therefore, absolute atmospheric pressure readings (QNH) obtained from nearby sources are considered, typically, more reliable than those provided by sources located farther away.

According to this invention, while the navigation device 10 is being transported along a road in reality, the navigation system 10 is equipped with wireless communication technology 18 capable of conducting an on-the-fly search for local absolute atmospheric pressure readings (QNH) such as from airports and other reliable sources. This search may include accessing the internet 20 and using a suitable search engine to find local atmospheric pressure readings (QNH) within some defined range of the instantaneous geo-position of the navigation device 10. For example, the system 10 may be configured to search the internet 20 for all QNH readings updated within the hour and issued by a source within a 50 km range. This is only an example of course, and other search criteria may be used. The navigation device 10, using coded logic, selects a reliable local atmospheric pressure reading (QNH) sufficiently near in geo-position to the instantaneous geo-position of the navigation device 10. An ambient actual atmospheric pressure measurement is also taken using the on-board altimeter 16. From the measured ambient actual and selected absolute pressure readings, a current elevation of the navigation device 10 above sea level can be calculated on the basis of a 0.12 mbar decrease in pressure for each 1 meter increase in elevation above sea level, thus eliminating the need for manual calibration as previously described. The calculation may, for example, include application of the following (or a similar) formula:

Current elevation (meters)=Selected absolute (mbar)−Measured ambient (mbar)/0.12

For example, if the navigation device 10 is transported in a motor vehicle which is traveling along a roadway in Amsterdam suitably near to Schiphol International Airport, a wireless internet search may find a reliable local absolute atmospheric pressure reading (QNH) at the website http://www.knmi.nl/actueel/metar.html, which provides QNH readings updated every thirty minutes. A real time query of this site in this example provides a current QNH reading of 1025 mbar. This represents the current atmospheric pressure at the Schiphol Airport adjusted to sea level. If the onboard altimeter 16 measures 1013 mbar, the previously provided calculation would yield:

Current elevation (meters)=1025−1013/0.12 12/0.12=100 meters

Accordingly, using this calculation together with the acquired local QNH reading obtained via a wireless search prompted by the navigation device 10, a current elevation of the navigation device 10 has been determined to be 100 meters above sea level. This current elevation is then associated with the corresponding instantaneous geo-position of the navigation device 10 for use in determining the position of the navigation device 10 in the digital road network. If the navigation device 10 happens to be traveling on one of two (or more) overlying roads in reality at the moment, the navigation device 10 can be mapped directly to a specific one of the two (or more) overlying roads based on the calculated current elevation of the navigation device 10, provided the digital map is appropriately attributed with road elevations. Through this technique, navigation assistance can be provided based on the calculated current road elevation of the navigation device 10. Advantageously, the accuracy of low-cost air pressure measuring equipment of the type incorporated into this invention will be sufficient to discriminate between various roads, and thus provide a reliable alternative to current high-cost solutions that rely on gyroscopic components.

It is foreseeable that, when conducting a wireless search for a reliable local atmospheric pressure reading (QNH), more than one reliable QNH reading may be found. Under these circumstances, the navigation system 10 may employ appropriate logic to select the most reliable one of the several offered QNH readings to be used in the elevation calculation. For example, the system may be configured to choose the closest source. Alternatively, the navigation system 10 may employ statistical techniques, such as averaging, to obtain a selected absolute pressure reading. For example, if two local QNH readings are obtained, one indicating 1,024 mbar and the other indicating 1,026 mbar, it may be appropriate to compute a simple average of 1,025 mbar to be used in the elevation calculation. To be even more precise, a weighted average may be taken as a good estimate, taking into account the relative distances and directions between the location of each QNH reading and the instantaneous geo-position of the navigation device 10. A weighted average will provide a more accurate linear approximation of the gradient of the pressure field. However, it is expected that deviations from linear will be small within a reasonable radius or range of about 100 km.

FIG. 6 is a highly simplified illustration of a four layer roadway which may, for example, exist in a typical parking garage. Vehicles fitted with navigation devices 10 according to this invention can calculate their current elevation so as to be placed on a specific road segment (i.e., level) in the parking garage. The navigation device 10 may then offer real time navigation assistance, provided details of the parking garage are contained in the onboard digital map or otherwise made available to the navigation system 10.

Turning now to FIG. 7, the concepts of this invention can be used, also, to help improve the accuracy and content of digital maps by recording road elevations. It is known that some GPS-enabled navigation devices 10 may be configured to passively generate probe measurements at regular intervals. Such probe traces typically comprise a sequence of geo-coded positions recorded at intervals of, for example, five seconds. These probe traces may be configured to include additional information, including metadata, which may include the calculated elevation of the roadway using the concepts of this invention. Collections of probe measurements can be taken for the purpose of incrementally updating digital maps. Such probe measurements can be transmitted either on-the-fly or subsequently to a collection service or other map data analysis service via wireless (e.g., cellular) transmission, via internet uploads, or by other convenient methods. FIG. 8 describes, in exemplary fashion, a longitudinal distribution of road elevations such as may be obtained through the passive collection of probe data using the on-the-fly elevation determinations of this invention. As a result, map database editors can use this information to improve and update the maps, which in turn may be effective to provide more accurate navigation and routing assistance.

The foregoing invention has been described in accordance with the relevant legal standards, thus the description is exemplary rather than limiting in nature. Variations and modifications to the disclosed embodiment may become apparent to those skilled in the art and fall within the scope of the invention. 

1. A method for providing real-time navigation assistance on land-based vehicular roadways using on-the-fly elevation determinations, said method comprising the steps of: providing a digital road map having a representation of a road network corresponding to a plurality of roads in reality, each road in reality having a measurable elevation above sea level at any given geo-position there along; providing a mobile navigation device interactive with the digital map, the navigation device capable of determining its instantaneous geo-position in the digital road network relative to the road in reality; transporting the navigation device along a road in reality while simultaneously updating its corresponding geo-position in the digital road network; conducting an on-the-fly search for local absolute atmospheric pressure readings (QNH) via wireless transmission; selecting a reliable local absolute atmospheric pressure reading (QNH); measuring the actual ambient atmospheric pressure; calculating a current road elevation as a function of the measured actual and selected absolute (QNH) pressures; and associating the calculated current road elevation with the corresponding instantaneous geo-position of the navigation device.
 2. The method according to claim 1 further including the step of updating the on-board digital map with the calculated elevation at the corresponding geo-position.
 3. The method according to claim 1 further comprising: transmitting the calculated elevation at the corresponding geo-position to a map update center.
 4. The method according to claim 1 wherein said selecting step includes computing the distance between the instantaneous geo-position of the navigation device and the geo-location of the local absolute atmospheric pressure reading (QNH).
 5. The method according to claim 1 wherein said step of selecting a reliable local absolute atmospheric pressure reading (QNH) includes comparing a plurality of available readings and choosing the closest in geo-position and time to the instantaneous geo-position of the navigation device.
 6. The method according to claim 1 wherein said step of selecting a reliable local absolute atmospheric pressure reading (QNH) includes linearly approximating the gradient of the air pressure field between the location of the local absolute atmospheric pressure reading and the instantaneous geo-position of the navigation device.
 7. The method according to claim 1 wherein said step of selecting a reliable local absolute atmospheric pressure reading (QNH) includes computing an average local absolute atmospheric pressure reading (QNH) from a plurality of data sources.
 8. The method according to claim 1 wherein said step of measuring the ambient atmospheric pressure includes making regular periodic passive samplings.
 9. The method according claim 1 wherein said step of calculating a current road elevation includes applying the formula: current elevation (in meters)=(selected absolute pressure (in mbar)−measured ambient pressure (mbar))/0.12.
 10. The method according to claim 1 wherein said step of conducting an on-the-fly search includes searching the internet.
 11. The method according to claim 1 further including the step of continuously updating the instantaneous geo-position of the navigation device in the digital road network relative to the road in reality based on data transmitted from a constellation of satellites.
 12. The method according to claim 1 further including the step of providing navigation assistance based on the calculated current road elevation.
 13. The method according to claim 1 wherein at least one road in reality overlies another road in reality but at an offset elevation, said step of associating the calculated current road elevation with the corresponding instantaneous geo-position of the navigation device includes associating the navigation device with a specific one of the two offset roads in reality; and providing navigation assistance based on the calculated current road elevation, said navigation assistance including mapping the navigation device to a specific one of the two offset roads in reality based, at least in part, on the calculated current elevation of the navigation device.
 14. A method for providing real-time navigation assistance on multi-level overlapping roadways using on-the-fly elevation determinations, said method comprising the steps of: providing a digital road map having a representation of a road network corresponding to a plurality of roads in reality, each road in reality having a fixed and measurable elevation above sea level at any given geo-position there along; at least one road in reality overlying another road in reality but at an offset elevation; providing a mobile navigation device interactive with the digital map, the navigation device configured to determine its instantaneous geo-position in the digital road network relative to the road in reality based on data transmitted from a constellation of satellites; transporting the navigation device along a road in reality while simultaneously updating its corresponding geo-position in the digital road network; simultaneously with said transporting step, conducting an on-the-fly search for local absolute atmospheric pressure (QNH) readings via wireless transmission; selecting a reliable local absolute atmospheric pressure reading (QNH) relatively near in geo-position and time to the instantaneous geo-position of the navigation device; measuring the ambient actual atmospheric pressure; calculating a current elevation of the navigation device above sea level as a function of the measured ambient actual and selected absolute (QNH) pressures; associating the calculated current road elevation with the corresponding instantaneous geo-position of the navigation device; mapping the navigation device to a specific one of the two overlying roads in reality at least partially based on the calculated current elevation of the navigation device; providing navigation assistance based on the calculated current road elevation; updating the on-board digital map with the calculated elevation at the corresponding geo-position by saving the calculated elevation as an attribute; and transmitting the calculated elevation at the corresponding geo-position to a map update center.
 15. A navigation device configured to perform the method of claim
 1. 